This invention relates to a pallet delivery system for a cam driven block machine and, in particular to, an independent pallet delivery system which reduces vibration to a pallet and hence optimizes formation and movement of a molded block, expedites the storage and handling of pallets and minimizes the wear on pallets that can result in down time caused by worn pallets.
In the early stages of concrete block manufacturing, concrete blocks were made in a single cavity mold by mixing sand, gravel and cement and then hand packing the mixture into a mold. When the material was packed at the proper consistency, the sides of the mold were folded down and the blocks were removed. Subsequently, the technology improved in the 1930's with the development of cam driven block machines. One such machine is described in detail in U.S. Pat. No. 2,692,418 and the basic process, thereof, which permits three molded blocks to be formed at one time has been and continues to be an industry standard.
Specifically, such cam driven block machines manufacture three standard eight inch blocks in an 8-10 second production cycle. These types of block machines are also capable of making different shapes and sizes of blocks. Concomitantly, block machines are powered by a ten to fifteen horse power electric motor through a clutching device and a series of gears which turn the main cam shaft of the machine. The cam shaft is formed with various other camming systems which operate functions that occur during each production cycle. The block machines further include shafts with arms and rollers that contact the cams. For example, one cam system operates the feed box coming out over the mold and fills the mold with a concrete mix. Another cam system allows the compaction head to drop onto the mold to compact the material. When the cement block is compacted, another camming system drops down a freshly made block (referred to commonly as green blocks), while another camming system permits the pallet receiver to receive the freshly made green blocks from the compacting head.
Another camming system comprised of shafts, cams, rollers, chains, lugs and sprockets cause the empty steel pallets upon which the green blocks are formed and delivered to enter the machine. These components define a dependent pallet delivery system. The dependent pallet delivery system of the cam driven block machine then transports the pallet to a position under the mold where the pallet receiver lifts the pallet from the dependent pallet delivery system and receives the freshly made green blocks on the pallet as the blocks are stripped out of the mold. The cam driven block machine then transports the pallet and the green blocks to a takeaway conveyer.
One disadvantage of the known pallet delivery systems is the fact that they are dependent on the rotation of the cams and shafts of the cam driven block machine to carry the pallet through the process of forming the blocks. The dependent pallet delivery system is provided with a magazine to store the pallets one on top of the other. Although this system has been used for decades in the industry, a number of problems in the manufacturing process occur due to the rough handling of both the pallets and the freshly made blocks.
First, as the empty pallet enters the pallet magazine, the empty pallet slams into other pallets in the magazine as well as the sides of the pallet magazines causing wear on the pallet magazine and the pallet itself. This slamming action is a noisy operation which repeats itself three to four thousand times a day in a typical manufacturing facility. More significantly, the vibration created from the slamming pallets is transferred to the freshly made green blocks being delivered to the conveyor transporting the green blocks. This vibration transferred to the block causes inherent weakness in the blocks as they are transported to the takeaway conveyor hence resulting in some cracked blocks being discarded before or after curing.
Another problem is caused by the manner in which pallets are moved through the machine to the mold area with a heavy chain having lugs. The chain and lugs contact the edge and the bottom of a pallet during transportation and also when the pallets are stacked in the pallet magazine. The chain and lugs then drag a pallet from under the stack into the machine area. During this operation, the pallet lugs create considerable wear and stress on the edges of the pallet. In addition, the heavy pallet causes wear on the magazine, and therefore the heavy chain and lugs also require a considerable amount of maintenance. Similarly, the engagement of the lugs and chain with the pallets also causes vibrations which are transferred to the green block. Further, as a result of the wear of both the pallet and lugs, on occasion, the lugs will not catch the pallet as each set of lugs are pulled down the conveyor. This will cause the block machine to complete the cycle with no pallet under the mold. As a result thereof, molded green blocks are dumped on the ground creating both a maintenance and clean up problem, in addition to a loss of material. Further, the pallet that is missed can jam in the machine which requires the machine to be shut down to remove the jammed pallet causing a decrease in operating efficiency. In addition, a jam in the machine may cause the timing bolt to shear requiring the entire system to be resynchronized.
The disadvantages noted above with respect to the known dependent pallet delivery systems are significant and represent an unsatisfactory mechanism that requires maintenance and impacts on the quality of the molded blocks. It is, therefore, desirable to provide an improved pallet delivery system, and more specifically, an independent delivery system which works independently of the cam driven block machine, but is timed to work integrally therewith to form blocks to overcome the disadvantages of the prior art.